The present invention relates generally to a stator assembly for an electric motor, alternator or generator, and, more particularly, to an improved phase coil insertion order for the stator assembly to reduce wind noise.
Generators are found in virtually every motor vehicle manufactured today. These generators, also referred to as alternators, produce the electricity necessary to power a vehicle""s electrical accessories and charge a vehicle""s battery. Generators must produce electricity in sufficient quantities to power a vehicle""s electrical system. Furthermore, generators must produce electricity having the characteristics necessary to be compatible with a vehicle""s electrical components. In addition, it is desirable for generators to produce as little noise as possible while operating.
A generator includes a stator and a rotor. In most generators, the stator consists of a metallic, magnetically-permeable core and one or more current-carrying stator windings in which voltages are induced by a changing magnetic flux. Typically, the core is an annular shaped structure. The internal circumference of the stator is formed with multiple tooth shaped protrusions separated by intervening slots. The stator winding is commonly formed by interconnecting three phase coils in a delta or wye connected arrangement. The phase coils are generally inserted into the slots and wound around the stator in one of a variety of known configurations called winding patterns.
In normal operation, the winding of the rotor is supplied with a current, which induces a magnetic flux in each of the rotor poles. As the rotor rotates, the flux generated at the poles cuts through the stator winding, generating an alternating current (AC) in it. The alternating current generated in the stator winding typically passes through rectifying circuitry before it is introduced into the electrical system of the vehicle.
The winding pattern of the stator winding and the configuration of stator teeth and slots are significant factors in the generator""s operating characteristics. Generator stators typically have one set of three-phase current carrying windings, but can have two or more stator windings. Each winding may consist of multiple coils each corresponding to a respective electrical phase p, of which there are typically three. As described above, wires that make up the stator windings are wound into the slots between adjacent stator teeth. Typically, the wire is wound around the stator teeth several times such that bundles of wire of the same phase are disposed in each slot.
One characteristic that the selected winding pattern affects is noise; both magnetic noise produced by the generator during operation and wind noise produced as a result of air flowing through and around the stator windings. The latter is due to a conventional, internal fan portion of the AC generator forcing air through the phase coil loops and ends. A so-called standard straight wave winding pattern is known; however, it exhibits poor mechanical tonal sound quality, particularly in the 6th, 12th and 18th orders harmonics.
U.S. Pat. No. 5,122,705 to Kusase et al. entitled xe2x80x9cALTERNATING CURRENT GENERATOR HAVING A PLURALITY OF INDEPENDENT THREE-PHASE WINDINGSxe2x80x9d discloses a winding pattern that purports to reduce wind noise. A 12-pole rotor is provided. A stator core is also provided having 72 teeth with 72 intervening slots. The stator core has a first three-phase stator winding (phase coils X, Y and Z) and a second stator winding (phase coils u, v, w) inserted into the slots in the following insertion order: X-u-Z-w-Y-v. It is believed, however, that such winding pattern nonetheless can be improved upon respecting wind noise.
In addition, a so-called reverse progressive (RP) winding pattern is also known that can reduce wind noise relative to a standard straight wave pattern. However, such a winding pattern requires a substantially more complex winding process. Specifically, a very complicated machine is required to wind a stator core in an RP winding pattern, and the cycle time is typically twice as long as other approaches.
There is therefore a need for a generator that minimizes or eliminates one or more of the problems set forth above.
One advantage of the present invention is that it substantially reduces airflow noise produced by the generator during operation. In one embodiment, the noise level is reduced by as much as 10 db (i.e., 18th order harmonic). This reduction in noise is obtained without any compromise in the cost, quality or performance of the generator.
The invention relates to the stator winding pattern used to configure a stator assembly. In particular, the invention involves a novel phase coil insertion order. A generator according to the invention includes a rotor having n magnetic pole pairs, a stator assembly having a core, first and second stator windings, and rectifiers. The stator core has a plurality 12*n of radially inwardly projecting, axially extending teeth with intervening slots. The first stator winding has first, second and third phase coils associated therewith. The second stator winding has fourth, fifth and sixth phase coils associated therewith. The rectifiers are coupled to the first and second stator windings for rectifying operating voltages generated in the windings. According to the invention, the first, second and third phase coils are sequentially wound on the core by being inserted in the slots in that order, such that respective starting leads of the first, second and third phase coils are progressively offset by n/3 stator teeth. In addition, the fourth, fifth and sixth phase coils are also sequentially wound on the core by being inserted in the slots in that order, after the first, second and third phase coils have been inserted, such that respective starting leads of the fourth, fifth and sixth phase coils are progressively offset by n/3 stator teeth.
In a preferred embodiment, n=6 (i.e., 12 magnetic rotor poles), the stator core includes 72 teeth with 72 slots, and the number of stator teeth that are offset (as defined above) is two. In a preferred embodiment, the first, second and third phase coils are three-phase, delta connected, as are the fourth, fifth and sixth phase coils. In a more preferred embodiment, the starting lead of the first inserted phase of the second set of stator windings is offset 85 degrees mechanical on the stator core relative to the starting lead of the first inserted phase of the first set of stator windings.
Other features and advantages will be apparent to those of ordinary skill in the art from the detailed description and accompanying drawings describing and illustrating the invention by way of example only and not by way of limitation.